1. Field of the Invention:
This invention relates to improvements in and concerning a system for the disposal of sewage (including excrements). It is particularly effective for use in a circulation type sewage disposal system such as a flush toilet on a railway vehicle.
2. Description of the Prior Art:
As disclosed in Japanese Utility Model Registrations No. 961449 and No. 961450 covering the inventions perfected by the same inventors, the conventional filter of this type has been intended for use in a circulation type sewage disposal system, which filter includes a filter proper having a multiplicity of slits formed in the peripheral surface thereof and also having the open end portions thereof rotatably set in position on a stationary seat, a suction pipe disposed to penetrate through and protrude upwardly from the interior of the filter proper and fastened to the stationary seat and scrapers laid outwardly from the axis of the filter proper and inserted into the grooves of the filter proper. The clear water passed through the filter is made to collect within the filter proper and it is then led through a suction pipe into the flush toilet for cyclic use. The suspended matter which has been deposited in the filtering spaces is removed by means of the scrapers to make the filter ready for reuse.
The filtering plates which make up the conventional filter of such a structure do not have a truly circular periphery but possess a periphery containing spaced protrusions each with a perforation for passing a clamping bolt (see FIG. 1). Moreover, the scrapers are not of a type slidably movable within a fixed range but of a type immovably fastened to a fixed shaft.
Despite the use of such stationary scrapers, the portions of the filtering plates which are designed to come into sliding contact with the scrapers must be formed in a circular shape in conformity with the overall loci of the motions of the scrapers since the scraping of deposited matter makes it necessary for the filter proper composed of a multiplicity of vertically spaced filtering plates to be rotated relative to the stationary scrapers. Consequently, it has been necessary to form protrusions outside the circular periphery of the filtering plates and bore perforations one each in the protrusions to permit passage of clamping bolts. Besides, since the scrapers are immovably positioned and are not allowed to move in the direction in which the filter proper rotates, a certain clearance must be allowed between the spacers inserted between the filtering plates and the scrapers in order to ensure smooth rotation of the filter proper.
In the conventional filter, therefore, the clearances prevent the filtering plates from coming into intimate contact with the scrapers, with the result that fibrous suspended matter is liable to lodge in the clearances. The fibrous suspended matter thus caught in the clearances gradually increases in bulk eventually to clog the filtering spaces. Furthermore, when the filter proper is rotated, the protrusions formed outside the filtering plates generate resistance and consequently form an eddy of fluid outside the filter proper and this eddy agitates the sewage particles which have already settled. Thus, the object of filtering cannot be fulfilled as originally contemplated.